The multiple images exposed by a multi-lens camera are a series of regular 2-D images of the same scene photographed at slightly different viewing angles. These regular 2-D images are necessary, as a group, for the composing of a 3-D print, but any one of them can also be used to produce conventional 2-D photographs. Logically, a multi-lens camera should be capable of being utilized as a 3-D camera or as a 2-D camera so that the consumer will not be required to have two cameras, one dedicated to 2-D picture taking and another dedicated to 3-D picture taking. However, all existing consumer 3-D multi-lens cameras adopt a half-frame negative format, and this format cannot cover the same field of view normally covered by a full-frame format used in a regular 35 mm full-frame camera.
3-D multi-lens cameras are designed to simulate the binocular vision of the human eyes. Therefore, in the design of a consumer 3-D multi-lens camera, the spacing between the two end most lenses should be kept roughly equal and not to exceed the separation distance between the eyes. This lens spacing is kept in order to assure a good 3-D effect and, at the same time, to avoid excessive parallax which causes a 3-D photograph to become out-of-focus. Since the eye separation distance of the average adult is between 63 and 70 mm, the preferred spacing between the two end most lenses in a consumer 3-D multi-lens camera should not exceed 70 mm, depending on the number of lenses on the camera. Furthermore, the distance between lenses in a multi-lens camera is also constrained by the size of the 3-D photograph, the normal viewing distance, and the distance of objects to be photographed.
In a multi-lens camera for stereoscopic photography, the center-to-center spacing between immediately adjacent lenses must be confined to the maximum acceptable distance for good viewing. This lens spacing must be kept within a parallax range so that the composite image in the 3-D photograph does not flicker or become out of focus. As disclosed in U.S. Pat. No. 5,059,771 (Ip et al.), the desired parallax, P, is computed according to the following equation: EQU P=(2V.pi./21600)E
where V is the normal viewing distance of the photograph, and E is the capability of the eyes to fuse together the two images of the stereo pair, expressed in terms of arc minutes of the scanning angle of the eyes. The constant 21600 is the number of arc minutes of a full circle (i.e., 360 degrees). It has been determined by empirical observation that E ranges from 20 to 10 arc minutes depending on the illumination and the contrast of the object in the scene. The normal viewing distance of the photograph is generally dictated by the size of the 3-D photograph and the normal viewing angle of the photograph. As disclosed by Ip et al, the viewing distance is given by: EQU V=D/[tan(.phi./2)]
where D is the longer dimension of the photograph and .phi. is the normal viewing angle which has been empirically determined to be about 15 degrees. With .phi.=15 degrees, we have tan(.phi./2)=0.132 and EQU V=3.79D
For example, with a consumer-size 3-D photograph of 3.5".times.4.5", D=4.5", D=4.5"=114.3 mm, the normal viewing distance V is approximately 12"-14" (i.e., 305 mm to 357 mm). If E is taken to be 6 arc minutes, then, with V=330 mm, we obtain ##EQU1## From this parallax value, one can calculate the required center-to-center spacing, T, between adjacent lenses according to an equation disclosed by Ip et al.: EQU T=BKP/u(B-K)
where u is the back focal length of the camera lens; B is the distance between the camera and background objects in the scene, and K is the distance of the key subject to be photographed. If the nearest allowable key subject distance from the camera is a 3 feet (i.e., 914 mm)and with the background so far away that B can be taken as infinity. For example, with a consumer camera that uses 30 mm lenses and a 135 film, the lens spacing is given by: ##EQU2## It should be noted that T is the center-to-center distance between adjacent lenses. If we allow for a small gap (e.g. 1 mm) between adjacent image frames, then the frame itself is 16.5 mm. For a camera using 35 mm film, this is roughly half the size of a regular full-frame format.
The above calculations show that it is not practical to design a multi-lens 3-D camera that takes full-frame images on the film planes behind all of the lenses on a camera using a 35 mm film. For this reason, all existing consumer 3-D cameras adopt a half-frame format as illustrated in FIG. 1. FIG. 1 clearly illustrates that the objectives 21, 22 and 23 will form images on frames 31, 32 and 33, respectively. The image frames are optically separated by baffles so that the image frames by one objective is only incident upon the corresponding frame or film plane.
It would be very advantageous for a consumer camera to be capable of exposing multiple images for 3-D photography and also provide a larger image format for 2-D photography. With such a design, the consumer will need only one camera for both 2-D and 3-D picture taking.